1. Field of the Invention
The present invention generally relates to a tire air pressure monitoring system. More specifically, the present invention relates to a tire air pressure monitoring system in which a tire air pressure decrease alarm is issued when tire air pressure data wirelessly transmitted by a transmitting device coupled to each tire of a vehicle indicates a tire pressure is equal to or less than a prescribed pressure.
2. Background Information
Japanese Laid-Open Patent Publication No. 11-334328 discloses a conventional tire air pressure monitoring system, which has recently been used by vehicle manufacturers. Such conventional tire air pressure monitoring system is configured and arranged to measure the tire air pressure by a pressure sensor installed in each tire of a vehicle, to convert the measured values into digital data, and to wirelessly communicate the data with a receiving system installed in the vehicle by using a high frequency transmission circuit after performing AM modulation or FM modulation to the data. The conventional tire air pressure monitoring system manufactured in Japan usually uses a frequency of 315 MHz for transmitting the data between the tire air pressure sensor and the receiving system.
The radio broadcasting regulations in one country may be different from the radio broadcasting regulations in the other country. Thus, a maximum frequency legally allowed to be used in transmission in one country may be different from a maximum frequency allowed in another country. For example, radio broadcasting regulations enacted in North American allow for a higher maximum output value in radio waves than the maximum output value allowed under Japanese radio broadcasting regulations. Therefore, if the conventional tire air pressure monitoring system is installed in a vehicle manufactured in Japan for exporting to North America, then the conventional tire air pressure monitoring system would have an output value from the high frequency circuit that complies with the output value established under the radio broadcasting regulations of North America. However, operating such configured conventional tire air monitoring system in Japan would violate Japanese radio broadcasting regulations. Therefore, the vehicle manufactures usually suspend transmissions from the tire air pressure sensor (transmitter) after installing the tire air pressure monitoring system in the vehicle in Japan. Then, the vehicle is exported to North America. When the vehicle arrives in a pier or wharf of North America, or a dealer or retail service station in North America, the each tire air pressure sensor is started up by using special startup tools. Alternatively, the tire air pressure sensor is started by rapidly decreasing the tire air pressure by releasing the tire air pressure which is kept in a high pressure in transit during exportation. The tire air pressure sensor detects the rapid change in the tire air pressure, and starts up the system from a resting state to a normal state.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved tire air pressure monitoring system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.